The invention is designed for use with a conventional rapid start fluorescent lighting fixture which has a plurality of tubes or lamps and employs a standard series-type ballast, e.g., one that is manufactured in accordance with specifications of the American National Standards Institute (ANSI). More particularly, the invention saves on the electrical energy normally required by such fixtures which are widely used in the illumination of industrial and commercial buildings. With the large amount of energy spent daily for lighting, there is great potential for energy conservation.
Attempts are presently made to conserve electrical energy consumed by a series of fluorescent lighting fixtures of a particular system of illumination by discriminately operating only a portion of the fixtures, or by the removal of lamps from the fixtures to drastically reduce the illumination of the fixtures. The results are usually unsatisfactory, since the design of the lighting system is radically altered, thereby resulting in spotty and uneven patterns of illumination. Moreover, the aesthetic appearance of the lighting fixtures is diminished and sometimes destroyed by the removal of any of the lamps.
As a solution to this problem, some manufacturers of fluorescent lamps have introduced a line of energy saving lamps which use a mixture of krypton gas. These lamps are more expensive than regular ones and the maximum energy savings for using them in conventional applications is estimated at only about 20% and, when such lamps are more highly loaded, there is little or no savings in the amount of electrical energy consumed.
So called phantom tubes have been tried. These devices produce no light and serve primarily to complete the circuit when two or more fluorescent tubes are used in series. As such, overall lighted lamp length and wattage of the fluorescent circuit is reduced accordingly. However, the overall efficiency of light production of the fluorescent circuit is also reduced. In addition, these tubes have the appearance of being burned out and thus detract from the pattern of illumination and the aesthetic appearance of the lighting fixtures where used.
More recently, there has been disclosed in U.S. Pat. No. 3,954,316, an electrical apparatus which is designed to modify the electrical circuit of a rapid start fluorescent lighting fixture to reduce power consumption of the fixture. A special D.C. isolation transformer is connected in series with the ballast and one of the lamp cathodes. A capacitor is wired across the primary and secondary coils of the transformer. This concept of isolating the lamp current and controlling it through reactive means is essentially what is taking place in the ballast itself. There are some disadvantages in using this apparatus. For example, the use of a D.C. isolation transformer tends to isolate the attached cathode from the normal starting ground plane which is established by the ballast. Starting potential between this cathode and the body of the fixture is essential to the reliable starting of any rapid start lamp. Moreover, the capacitor is wired across the windings of the isolation transformer and therefore remains charged after power to the fixture is turned off. This situation could prove hazardous to anyone repairing the ballast or lamp circuits. Finally, the use of a single capacitor across the transformer windings can result in significant differences in cathode voltage, depending on how the apparatus is connected in the circuit.
My invention is directed to an electrical device which overcomes the problems mentioned above, and which is safer and more reliable to use.